In all cellular communications networks there are opposing requirements for high spectrum efficiency and high area availability, or coverage. As a Fourth Generation (4G) technology, Long Term Evolution (LTE) is expected to provide high spectrum efficiency. Namely, LTE is expected to provide three to four times higher spectrum efficiency than High-Speed Downlink Packet Access (HSDPA) Release 6 for the downlink, and two to three times higher spectrum efficiency than High-Speed Uplink Packet Access (HSUPA) Release 6 for the uplink. In addition, as with any cellular communications network, LTE must provide 90%-95% coverage, which is referred to as Carrier Grade of Service (CGOS) for coverage. The requirements for high spectrum efficiency and coverage are opposing in that a small frequency reuse factor (N) is desired in order to achieve high spectrum efficiency but, in general, a high frequency reuse factor (N) is desired in order to decrease out-of-cell interference and therefore increase coverage. A maximum spectrum efficiency is achieved when the frequency reuse factor (N) is 1, such that the entire spectrum is reused in each cell of the cellular communications network. However, when the frequency reuse factor (N) is 1, out-of-cell interference is at its maximum and, therefore, coverage is at its worst.
Spectrum efficiency can be roughly determined by a minimum Signal-to-Interference-plus-Noise (SINR) needed for a wireless communication link, or airlink, to survive in the cellular communications network. For example, an Advanced Mobile Phone System (AMPS) typically requires a SINR of greater than or equal to +18 decibels (dB). Thus, in order to achieve the CGOS in AMPS, a very large frequency reuse factor of N=21 is needed in order to achieve the needed SINR. As another example, a Code Division Multiple Access (CDMA) system can operate with SINR values as low as −14 dB as a result of the processing gain due to the spreading and dispreading process. Therefore, a frequency reuse factor of N=1 can be used in the CDMA system.
For LTE, a minimum SINR needed to maintain a wireless communication link is approximately −5 dB. However, for a fully loaded LTE network having a frequency reuse factor of N=1, test results show that the SINR at cell edges can be lower than −12 dB. Therefore, there is a need for a system and method for improving coverage in an LTE cellular communications network while maintaining high frequency reuse.